1. Field of the Invention
This invention relates to blends of grafted polyacrylate rubber with other polymers. More specifically it relates to blends of (1) a first grafted rubber polymer wherein the rubber has a core/shell structure where the core is a styrenic polymer and the shell is an acrylate rubber; (2) a second grafted rubber polymer wherein the rubber is selected from the group consisting of diene, ethylene propylene and acrylate rubbers; and (3) a matrix polymer formed from a vinyl aromatic monomer, an unsaturated nitrile monomer and optionally one or more compatible comonomers.
2. Description of Related Art
Polymer blends of grafted rubbers are well known in the prior art. These blends are especially useful as molding and extrusion compositions for indoor and outdoor applications. The blends have good impact and weatherability properties. Blends of various polymers using one or more core/shell type polymers are also known. They are taught in the following patent publications.
EPO Patent Publication 0 534 212 A1 (BASF) teaches a mixture of (1) a graft copolymer having a core of a 50-99.9% by weight of a vinylaromatic monomer with a polyfunctional crosslinker and/or a comonomer with two or more functional groups; and (2) a graft polymer having a rubbery core and a shell having a Tg&lt;25.degree. C.
EPO Patent Publication 0 342 283 (Rohm & Haas) teaches either thermoplastic or thermoset matrix polymers and substantially spherical polymer particles having an average diameter of from 2 to 15 micrometers.
U.S. Pat. No. 4,916,171 to Brown et al teaches core/shell polymers having an alkali-insoluble, emulsion polymer core and an alkali soluble, emulsion polymer shell attached or associated with said core so that upon dissolving said shell with alkali, a portion of said shell remains attached or associated with said core. Also taught are compositions wherein said shell polymer has been neutralized and substantially, but not totally, dissolved so as to form a blend of neutralized core-shell polymer and an aqueous solution of neutralized shell polymer.
U.S. Pat. No. 5,047,474 to Rabinovich et al teaches modifier compositions of acrylic core/shell polymers and alkyl methacrylate-butadiene-styrene core/shell polymers are added to polyvinyl halides to provide materials with improved color depth and impact strength, as well as reduced pearlescence.
U.S. Pat. No. 5,237,004 to Wu et al teaches polymer particles in a size range between 2 and 15 micrometers, and having a refractive index close to, but not identical with, that of a matrix polymer and optionally having one or more enclosing shells, the outer shell being compatible with the matrix polymer, impart light-diffusing properties to the matrix polymer without degrading its physical properties, while the particles having a closer refractive index match to the matrix polymer impart gloss reduction to the surface of the matrix polymer.
U.S. Pat. No. 5,266,610 to Malhotra et al teaches the use of core/shell particulate toughening agents in a composite resin system comprised of thermoplastic and thermoset resins wherein the phase morphology is cocontinuous.
Japanese Patent Publication 62/236,850 to Takeda Chemical Industry teaches a core/shell type structure where the glass transition temperature of the core is higher than that of the shell for use in motor vehicles. The blends of grafted rubbers of the prior art are maybe useful. However they may be difficult to color and lack the balance of properties provided by the blends of the present invention. For example, in the prior art blends of (1) a polybutylacrylate rubber grafted with styrene and acrylonitrile (ASA); and (2) a butadiene rubber grafted with styrene and acrylonitrile (ABS), the polybutylacrylate (PBA) used in the ASA component has a lower refractive index (RI) than the polybutadiene (PBD) used in the ABS which has a lower RI than SAN which is grafted onto the polybutylacrylate and polybutadiene and which is also present in the blends as a free matrix polymer. Thus, the difference in RI between the ASA component and the ABS component causes the ASA/ABS blends to be opaque and more difficult to color than ABS alone.